FIG. 1 is a diagram showing the configuration of a power source system disclosed in Japanese Patent Application Publication No. 2013-046454 (hereinafter “JPA '454”; see, e.g., FIG. 1, FIG. 2). The power source system shown in FIG. 1 is constituted by a three-phase commercial power source E, a DC (direct current) power source apparatus 501 and a load RL, and of these, the DC power source apparatus 501 is constituted by a power storage apparatus 60, a plurality of DC power source apparatus units 1 to N, one charging/spare unit, and a monitoring unit 81 including an operational state determination unit 82, an output voltage monitoring unit 83, a droop operation control unit 84, a charging voltage detection unit 85 and a constant-current charging control unit 86.
During a normal operation, the DC power source apparatus 501 operates n DC power source units 1 to N and supplies power to the load RL having constant power characteristics, and if there is a fault in any one of the DC power source units 1 to N, the charging/spare unit is used as a substitute unit for the unit suffering a fault. In the example illustrated, three-phase AC power is used as the input power source, but a configuration in which a single-phase AC power is used as the input source may also be used.
When an AC input from the commercial power source E is lost due to a power outage, power is supplied to the load RL from a storage battery 61 via a diode DX1. Furthermore, in this DC power source apparatus 501, the charging/spare unit, as well as being used as a spare power source unit, also serves as a charger for the storage battery 61.
When an output voltage is supplied to the load RL from the DC power source units 1 to N, since the charging/spare unit and the storage battery 61 are separated from the load RL side, a reverse bias voltage is applied to the diode DX1.
The DC power source units 1 to N and the charging/spare unit have constant-current droop characteristics which limit the output current to a prescribed rated current (100% continuous rated current), in order to prevent damage to the units, during normal operation, and the constant-current droop characteristics can be switched temporarily to constant-power droop characteristics in the event of prescribed trigger conditions (conditions which are set in accordance with the operational state of the DC power source apparatus 501), for example, in the event of trigger conditions such as power source recovery after a power outage.
A voltage sensor VT1 detects the output voltage Vo (=load voltage VL) of the DC power source apparatus 501. The voltage sensor VT2 detects the charging voltage of the storage battery 61. A current sensor CT1 detects the charging current of the storage battery 61.
A monitoring unit 81 communicates with the DC power source units 1 to N and the charging/spare unit, and monitors the operational state of the DC power source units 1 to N and the charging/spare unit, as well as sending a control command signal (for example, a droop characteristics switching command signal) to the DC power source units 1 to N and the charging/spare unit.
The operational state determination unit 82 receives input of operational state signals St1 to StN from the DC power source units 1 to N, and receives input of an operational state signal Stc from the charging/spare unit. Consequently, the operational state determination unit 82 detects (determines) the operational state of the DC power source unit and the charging/spare unit, the occurrence of and recovery from faults, and restoration of power after a power outage, and the like.
On the basis of the operational state signals received from the DC power source units 1 to N and the charging/spare unit, the operational state determination unit 82 determines whether the system is in a normal operational state in which all of the units are operating normally, for example, or a start-up state after restoration of power from a power outage, or a state of starting operation after recovering a DC power source unit that has suffered a fault.
The output voltage monitoring unit 83 receives input of a voltage detection signal from the voltage sensor VT1 and monitors the output voltage Vo of the DC power source apparatus 501. Furthermore, the droop operation control unit 84 controls the droop characteristics of the DC power source units 1 to N and the charging/spare unit, in accordance with the state of operation of the DC power source units 1 to N and the charging/spare unit. Moreover, the charging voltage detection unit 85 receives an input of a voltage detection signal from the voltage sensor VT2 and monitors the charging voltage of the storage battery 61.
The constant-current charging control unit 86 controls the charging/spare unit so as to perform a constant-current output operation, when carrying out constant-current charging from the charging/spare unit to the storage battery 61. During the constant-current charging described above, the constant-current charging control unit 86 in the monitoring unit 81 performs constant-current charging to the storage battery 61 by controlling the output current of the charging/spare unit. In this case, the constant-current charging control unit 86 detects the charging current flowing to the storage battery 61 by the current sensor CT1 and controls the output current of the charging/spare unit so as to become a prescribed constant current value. In the power source system disclosed in JPA '454, a plurality of DC power source units are connected in parallel, the output line thereof is backed up by a battery during a power outage, and the droop characteristics of the power source unit are controlled so as to supply current at or above a rated current, temporarily.